than one unit with four busses attached to it. This allows us to use
existing fdt data which describes separate devices with separate resources.
It also allows any combination of the units to be en/disabled in the
board dts files.
Adjust our dts code to match what's used by linux and u-boot now that
we're structured to do so.
Document lots of interesting stuff learned whiling doing this with a big
comment block in the driver, so I don't have to re-learn it for the next
round of changes.
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